The present invention relates to the field of stent crimping devices generally, and more particularly, to a device for providing a grooved crimp which is generally parallel to the axis of a stent.
Stents are typically used as adjuncts to percutaneous transluminal balloon angioplasty procedures in the treatment of occluded or partially occluded arteries and other blood vessels. In a typical balloon angioplasty procedure, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is positioned at a point proximal to the lesion site. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressure to radially compress the atherosclerotic plaque of the lesion and increase the diameter of the occluded artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and blood flow resumed through the dilated artery. As will be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Balloon angioplasty sometimes results in short or long term failure. Vessels may collapse abruptly shortly after the procedure or a gradual narrowing of the vessel (restenosis) may occur for several months thereafter. To counter the tendency of recurrent vessel occlusion following angioplasty, implantable intravascular prostheses, commonly referred to as stents, have emerged as a means by which to achieve long term vessel patency. A stent functions as permanent scaffolding to structurally support the vessel wall and thereby maintain lumen patency. Stents are typically small expandable cylindrically-shaped devices which have a generally open cellular construction. Stents usually are transported to a lesion site by means of a delivery catheter.
There are two general classes of stents namely, balloon expandable stents and self-expandable stents. Balloon expandable stents are delivered in a small diameter or low profile configuration by means of a balloon catheter and are plastically deformed to a second larger diameter by means of an inflation balloon. Self-expanding stents are formed as spring elements which are radially compressible about a delivery catheter. A self-expanding stent is typically held in the compressed state by a delivery sheath. Upon delivery to a lesion site, the delivery sheath is retracted allowing the stent to expand.
Details of balloon expandable stents can be found in U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No. 5,421,955 (Lau et al.); U.S. Pat. No. 5,603,721 (Lau et al.); U.S. Pat. No. 4,733,665 (Palmaz); No. 4,739,762 (Palmaz); and U.S. Pat. No. 5,569,295 (Lam). These patents describe a few typical examples of the more common types of balloon expandable stents. There are many other designs which have been developed.
Stent crimping devices often are used to secure balloon expandable stents to the inflation balloons of stent-delivery catheters. A stent is first loaded and then crimped onto the balloon portion of a stent delivery catheter. The stent-delivery catheter is advanced to a position where the stent crosses the arterial lesion. The balloon is inflated causing the stent to expand to its deployed diameter for implantation in the artery wall. To ensure proper deployment, the stent must be securely mounted on the balloon portion of the delivery catheter. If the stent should slip on the balloon during delivery, nonuniform deployment may result. In this situation, the stent may partially occlude the artery, thereby worsening the condition that the stent is intended to repair. Occasionally, stents have slid completely off of the balloon and have migrated downstream in the patient""s artery, sometimes necessitating emergency removal procedures. Thus, the problem of stent slippage on delivery catheters is a serious concern to vascular surgeons.
In the past, stents have been crimped onto catheter balloons by hand, often with the aid of small tools such as sterile pliers, or by machines built specifically for crimping. Many prior art devices have been directed towards achieving what is referred to as a xe2x80x9croll crimpxe2x80x9d of the stent onto the balloon, i.e., the stent is uniformly compressed about the balloon portion of the delivery catheter. Problems commonly associated with hand-crimping include non-uniform crimping, the inability to determine if a reliable crimp has been achieved, and physical damage to the stent which can be easily overlooked by visual inspection and can cause the stent to expand improperly within the patient.
Several devices have been developed in an attempt to address these problems. One such device is described in U.S. Pat. No. 5,437,083, entitled xe2x80x9cStent Loading Mechanism,xe2x80x9d issued to Williams et. al, Aug. 1, 1995. The Williams device utilizes a series of plates which have substantially flat and parallel surfaces that move in a rectilinear fashion with respect to each other. A stent is slipped over the balloon portion of the delivery catheter and the strut is placed between these surfaces. The stent is roll crimped onto the balloon by relative motion of the plates. The Williams device has been successful in producing a uniform roll crimp.
Machine crimped stents with roll type crimps have proven to be reliable as well. However, in certain circumstances, such as when the stent encounters obstacles such as hardened plaque or a flap of tissue partially torn from a vessel wall, roll crimped stents occasionally will still move or slide off of the delivery catheter. It is believed that this slippage problem may continue to occur because a stent uniformly crimped along its length forms a somewhat smooth continuous interface with the balloon and may not always generate sufficient frictional resistence to remain positioned on the balloon, especially when subjected to external forces created when delivering the stent within the patient""s vasculature.
Typical materials used for the balloon portion of a delivery catheter include polyester, polyamide, and polyolefin, all of which usually exhibit a relatively low coefficient of friction, when bearing against a metallic structure such as a stainless steel stent. Therefore, in situations where maximum stent security is required, what is needed is a stent crimping device that will create regions of high frictional resistance between the stent and the balloon, thereby improving stent security on the balloon.
The stent crimping device of the present invention has three main components, an inner hub, an outer hub, and a plurality of radially inwardly sliding jaws which engage the stent. The inner hub includes means for retaining the sliding jaws and also includes spring-loaded push rod assemblies which bias the jaws radially outwardly to an open position. Each jaw includes a crimping surface for forming a selected type of crimp. The crimping surface may have several profiles including, but not limited to, V-shaped, U-shaped, and flat surfaces. The outer hub is rotatably engaged over the inner hub and encloses the sliding jaws. The outer hub includes an opening which guides and centers the stent-delivery catheter between the sliding jaws. Rotation of the outer hub causes the slidable jaws to move radially inwardly so that the jaws engage and securely crimp a stent to the expandable member of the stent-delivery catheter. Rotation of the outer hub in the reverse direction allows the spring-loaded push rods to bias the jaws radially outwardly thereby releasing the crimped stent. The stent crimping device may be used for on-site crimping of stents to delivery catheters at a medical facility or may be readily adapted for mass production of pre-crimped stent-delivery catheter assemblies.
The crimping device of the present invention can provide at least two general types of stent crimps. In one form, the stent crimp is composed of a plurality of spaced grooves which run the longitudinal length of the stent. The number and spacing of the grooves will vary depending on the size and type of stent. In a second form, the stent crimp is composed of a plurality of radial indentations spaced along the body of the stent. The spacing of the indentations may vary both radially around the circumference of the stent and longitudinally along the length of the stent. Both the grooved type crimp and the radial-indentation type crimp deform the stent so that it engages the balloon material to create regions of high frictional resistence between the metal struts of the stent and the expandable member of the stent delivery catheter. The regions of high frictional resistence created by the crimping device generally affix the stent to the balloon more securely than a roll type crimp.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.